1. Field of the Invention
The present invention relates to a transfer arm apparatus for transferring a target substrate, such as a semiconductor wafer or an LCD substrate, and a semiconductor processing system using the transfer arm apparatus. The semiconductor process includes various kinds of processes which are performed to manufacture a semiconductor device or a structure having wiring layers, electrodes, and the like to be connected to a semiconductor device, on a target substrate, such as a semiconductor wafer or an LCD substrate, by forming semiconductor layers, insulating layers, and conductive layers in predetermined patterns on the target substrate.
2. Description of the Related Art
In a process of manufacturing a semiconductor device, a transfer arm apparatus is used for loading and unloading a target substrate to and from a process chamber. FIG. 9 is a plan view schematically showing the structure of a transfer arm apparatus 90 which is conventionally typical. The transfer arm apparatus 90 has a first arm 91 capable of bidirectionally pivoting, a second arm 92 pivotally connected to the distal end of the first arm 91, and third arm 93 pivotally connected to the distal end of the second arm 92. A target substrate, e.g., a semiconductor wafer is transferred while it is mounted on the distal end of the third arm 93. The first and second arms 91 and 92 contain pulley mechanisms (not shown), with which the second and third arms 92 and 93 can be bent and stretched.
Since the transfer arm apparatus 90 is designed to transfer only one target substrate, i.e., one wafer, at a time, the process chamber cannot be efficiently loaded and unloaded with wafers, and a limit is brought about improving throughput. Accordingly, if the third arm is modified to have two wafer support portions, one on either end, in order to transfer two wafers together by the third arm, the throughput can be improved. However, where this modification is applied to the transfer arm apparatus 90, the following problems arise.
Specifically, in this case, the third arm needs to be connected, by its central portion in the longitudinal direction, to the distal end of the second arm, in order to allow the wafer support portions at opposite ends of the third arm to be equivalently usable. Since the length of the third arm should not be so large in light of its operation space, that distance from the connecting portion between the second and third arms to each of the wafer support portions at opposite ends of the third arm inevitably becomes short. As a result, upon transferring a wafer to and from a process chamber, the connecting portion between the second and third arms has to enter the process chamber. When the connecting portion of the arms enters the process chamber, in which the temperature may be at least 1000.degree. C., part of the pulley mechanism at the connecting portion is damaged by the high temperature.
More specifically, the pulley mechanism is usually surrounded by a casing and the connecting portion of the arms is vacuum-sealed by an airtight structure formed of a magnetic fluid seal to prevent the wafer from being contaminated with particles and impurity gases generated from the pulley mechanism and belts. Since the magnetic fluid seal is apt to be degraded by heat, when the connecting portion between the second and third arms are exposed to the high temperature, the airtight structure of the magnetic fluid seal is degraded and damaged, and so are the belts of the pulley mechanism.
On the other hand, there is a conventional transfer arm apparatus of another type, which has first and second arms respectively formed of link mechanisms. The transfer arm apparatus of this type requires a number of links to be used, thereby bringing about a difficulty in providing a structure suitable for a narrow and low-height space, such as a transfer chamber. In addition, since the link mechanisms each have a change point, i.e., a dead point, the first and second arms can be hardly stretched out. When the link mechanisms are stretched up to a near dead point, the first and the second arms become unstable in its posture and can hardly transfer a wafer to a predetermined position, e.g., a wafer chuck, in a process chamber. Further, the transfer arm apparatus of this type cannot provide a sufficient transfer stroke in spite of the length of the first and second arms.